1. Field of the Invention
The present invention relates to a pallet for handling dental porcelain materials, which is used to prepare procelain crowns such as porcelain crowns with metals baked to them and porcelain jacket crowns, and always keeps the consistency of a dental porcelain slurry constant for successful porcelain handling.
2. Prior Art
Heretofore, porcelain crowns such as porcelain crowns with metals baked thereon and porcelain jacket crowns have been prepared by placing a suitable amount of the dental porcelain powders used upon a porcelain kneading pallet (hereinafter called simply the pallet), adding thereto a suitable amount of distilled water or a kneading liquid exclusive to porcelain materials (hereinafter referred simply to the kneading liquid), kneading them with a metallic spatula or the like into a slurry having a certain consistency, and placing a suitable amount of the dental porcelain slurry on a metal frame or model with the use of a brush, a metallic spatula or the like for firing or calcination.
Hitherto, glass plate, Teflon plate or vitreous china plate with glaze put on their surfaces have been used as the kneading pallets for mixing the dental porcelain powders with distilled water or the kneading liquid into a dental porcelain material slurry and preserving it until it is used for dental handling.
When porcelain crowns such as porcelain crowns with metals baked thereon and porcelain jacket crowns are to be prepared, however, the distilled water or kneading liquid, contained in the dental porcelain material slurry preserved on the pallet, diffuses slowly in the air, so that the slurry can be dried or solidfied within a few minutes to about 10 minutes to such an extent that it cannot be handled, thus making it impossible to place it on the metal frame, etc. with a brush or metallic spatula. Consequently, the dental porcelain slurry should again be kneaded with a suitable amount of distilled water or the kneading liquid. This was troublesome and inconvenient because dental handling could not stably be carried out at a certain consistency.
There have been some dental porcelain material kneading pallets designed to supply distilled water or the kneading liquid to a dental porcelain material on a dental porcelain material kneading plane by some means. As one of such pallets, there has been proposed a dental porcelain material kneading pallet (Japanese Patent Application No. 42588/1979, entitled "MIXING TRAY ASSEMBLY") which comprises a vitreous china plate with glassy glaze put on its surface and an opening formed in its dental porcelain material kneading material plane and a cotton core passed through said opening, as is the case with an alcohol lamp's wick, thereby sucking up distilled water or a kneading liquid exclusive to dental porcelain materials from the bottom of the pallet. A grave problem with this assembly has been that the distilled water or kneading liquid penetrates only through the core's periphery of the kneading plane, thus failing to make the whole dental porcelain slurry have a certain consistency.
Other dental porcelain material kneading pallets have been available, in which no glassy glaze is put on a part of a dental porcelain material kneading plane of a vitreous china plate located on the upper face of a closed case, or pores of about 1 mm in diameter are provided in the kneading plane, thereby sucking up distilled water or a kneading liquid exclusive to porcelain materials due to a water pressure difference owing to a difference in height between the liquid level in an inlet hole and the kneading plane. A grave problem with these has been that because the distilled water or kneading liquid is caused to ooze out on the kneading plate due to a difference in height between the liquid level in the inlet hole and the kneading plane, the liquid level in the case is so likely to change that there can be a drop of the liquid pressure, which in turn makes the oozing of the distilled water or kneading liquid onto the kneading plane unstable and so makes it impossible to impart a certain consistency to the dental porcelain material slurry.
More recently, a dental porcelain material kneading pallet having only a portion of its upper face, on which a dental porcelain material is to be kneaded, left intact with no glaze put thereon, i.e., unglazed has been proposed for a conventional dental porcelain material kneading pallet formed of porcelain and having its overall surface made smooth by putting glassy glaze thereon. This pallet formed of porcelain is placed on a tray through sponge. Then, distilled water or the kneading liquid is charged in the tray to a height of about 5 mm from the tray's face, whereby it is sucked from the bottom of the pallet into the body of the pallet through the sponge and then reaches the dental porcelain material kneading portion defined by the upper face of the pallet. Thus, the distilled water or kneading liquid is supplied to the kneaded dental porcelain slurry, thereby assuring that its consistency is always kept constant.
However, such a dental porcelain pallet has posed various difficult-to-solve problems, as mentioned below.
(1) For the very reason that it is formed of vitreous china and partly left intact or unglazed, its surface is so rough, as expressed in terms of a centerline surface roughness of 15 .mu.m, that the dental porcelain slurry can be brushed out with difficulty and that the brush is prematurally worn down.
(2) For the same reason that its surface is very rough, a metallic spatula used for mixing the dental porcelain powders with distilled water or the kneading liquid is so likely to be worn down by contact with the porcelain's surface. Powders resulting from the abrasion of the metallic spatula or the pallet may contaminate the dental porcelain slurry to make the prepared porcelain crown cloudy.
(3) The pallet is formed of a conventional vitreous china material with no modification made to it, so that it differs largely in particle size, i.e., has a very wide particle size distribution. In consequence, the porcelain pallet varies so largely in pore diameter that the penetration of distilled water or the kneading liquid from the bottom of the pallet to the porcelain material kneading plane becomes unstable, thus making it difficult to keep the consistency of the dental porcelain slurry constant and hence dental handling is made difficult.
(4) As stated in (3), the dental porcelain pallet varies so largely in pore diameter that it varies in porosity from place to place or, to put it another way, pores are not uniformly dispersed throughout the pallet. For that reason, insufficient penetration of distilled water or the kneading liquid is more likely to occur on the pallet's ends than the pallet's central region. This results in the consistency of the dental porcelain slurry becoming uncertain and so often needs repeated kneading, which makes its dental handling difficult.
(5) When the porcelain pallet is immersed in distilled water, etc. over an extended period of time, it becomes unhygienic since its kneading plane is covered with mold due to its large pore diameter.
(6) In use, sponge is placed as a cushion between the porcelain pallet and the case so as to suck up moisture through the pallet in a stable manner. Since the pallet is overlaid on the sponge so that it is spaced away from the case, however, it tends to be so unstable when the dental porcelain slurry is kneaded or brushed out that its dental handling becomes difficult.
A primary object of the present invention is to provide a solution to the above problems which make it impossible to carry out dental handling and to prepare porcelain crowns in a rapid and effective manner, whereby the problems of the conventional water-permeable dental porcelain material-handling pallets that they have uneven pore sizes, not uniform pore size distribution and large surface areas can be eliminated successfully. In consequence, it is unlikely that metallic spatulas or pallets may be worn down at the time of kneading dental porcelain slurries and it is assured that the dental porcelain slurries are well brushed out with no abrasion of the brushes, thus making it possible to carrying out dental handling in speedy manners.